WO2021166651A1

WO2021166651A1 - Radiant tube

Info

Publication number: WO2021166651A1
Application number: PCT/JP2021/003974
Authority: WO
Inventors: 知之川島; 祥大小林; 典子小澤
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2020-02-21
Filing date: 2021-02-03
Publication date: 2021-08-26

Abstract

Provided is a radiant tube that is of a simplified structure and that has a heat transfer enhancement body capable of achieving a higher heat-transfer efficiency. A heat transfer enhancement body (4) comprises: a body part (41) that is disposed on the center side of a pipeline (1); and a plurality of projecting parts (42) that protrude from the body part (41) toward the inner wall surface (1a) of the pipeline (1). The plurality of projecting parts (42) are formed on the outer circumference of the body part (41) so as to be arranged in the circumferential direction of the pipeline (1). Said projecting parts (42) include a plurality of first projecting parts (42a) opposing the inner wall surface (1a) of the pipeline (1) across a gap (ΔL) with the remainder being second protruding parts (42b). The first projecting parts (42a) are provided in a quantity greater than that of the second projecting parts (42b). When the ratio (ΔL/Dt) of the gap to an equivalent diameter of the pipeline (1) portion where the heat transfer enhancement body (4) is disposed is defined as x[%] in percentage, expression 0.3%<x<7% is satisfied.

Description

Radiant tube

The present invention relates to a radiant tube having a heat transfer promoter.

The radiant tube includes a pipeline constituting the tube body and a gas generating portion such as a burner arranged on the inlet side of the pipeline to generate combustion gas. The radiant tube indirectly heats the object to be heated outside the pipe by the radiant heat from the pipe heated by the combustion gas generated by the gas generating part.
In the radiant tube, the combustion gas generated by the gas generating portion flows along the gas flow path formed in the pipeline. As a result, the pipeline becomes hot due to heat transfer from the combustion gas. At this time, in the radiant tube, heat transfer from the combustion gas to the pipeline progresses, and on the outlet side (downstream side) of the pipeline where the temperature of the combustion gas decreases, the amount of radiant heat transfer decreases and the surface temperature of the pipeline rises. descend. Therefore, in order to increase the heat transfer efficiency from the combustion gas to the pipeline on the downstream side (outlet side) of the radiant tube and increase the heat utilization rate of the radiant tube, heat is transferred to the downstream side of the pipeline. A promoter may be installed.

For example, in Patent Document 1, a heat transfer promoter is arranged in the latter half of the pipe line of the radiant tube, and as the heat transfer promoter, a plate-shaped guide blade that spirals the flow path of the combustion gas is provided. The configuration is disclosed. According to this technique, in the latter half of the radiant tube pipeline, the combustion gas is swirled in a spiral and flows to the outlet of the pipeline to increase the relative velocity between the pipeline and the combustion gas. Increase the convection heat transfer coefficient.
However, in the method described in Patent Document 1, the structure of the heat transfer promoter needs to have a complicated shape in order to swirl the combustion gas in a spiral shape. Therefore, the heat transfer promoter described in Patent Document 1 has a high manufacturing cost, and a cheaper heat transfer promoter is required.

On the other hand, in Patent Document 2, a heat transfer promoter having a cross-shaped cross section having four plate-shaped partitions is provided, and the heat transfer promoter having a cross-section cross-section is changed in phase by 45 degrees. It is disclosed that a plurality of pieces are inserted in series in a pipeline. According to this configuration, since a plurality of heat transfer promoters are fitted and inserted in the conduit, a spiral air flow can be formed at low cost. However, it cannot be said that the heat transfer promoter having a cruciform cross section described in Patent Document 2 has sufficiently high heat transfer efficiency, and further improvement has been required.
Further, Patent Document 3 defines the ratio between the cross-sectional area of the heat transfer promoter and the cross-sectional area of the radiant tube, the peripheral length of the cross section of the heat transfer promoter, and the ratio to the peripheral length of the cross section of the radiant tube, and defines the heat transfer efficiency. A star-shaped heat transfer promoter that can be manufactured at low cost by suppressing the increase in pressure loss due to the insertion of the heat transfer promoter has been proposed.

Japanese Patent Application Laid-Open No. 57-112694 Jikkai Sho 63-173613 Japanese Unexamined Patent Publication No. 2017-83127

The technique of Patent Document 3 aims to improve the heat transfer coefficient by reducing the flow path area. With this technique, the gas flow velocity in the flow direction along the pipeline is improved. However, in this technique, since the tip of the protrusion forming the heat transfer promoter is in contact with the inner wall surface of the pipeline, the cross section of each flow path formed between the adjacent protrusions is divided. The flow in the turning direction is suppressed.
That is, in Patent Document 3, although the shape of the heat transfer promoter can be manufactured simply and inexpensively, it is not possible to obtain a large heat transfer coefficient by that amount due to the division of the cross sections of the individual flow paths. Further, in Patent Document 3, when considering the actual operation of the radiant tube, a deformation allowance considering the thermal deformation of the radiant tube and the heat transfer promoter is also required.
The present invention has been made in view of the above points, and an object of the present invention is to provide a radiant tube having a heat transfer promoter having a simple structure and capable of further improving heat transfer efficiency.

The inventors performed a numerical simulation comparing the heat transfer efficiency from the waste heat reduction rate of the radiant tube for the shape of the heat transfer promoter having a plurality of protrusions as in Patent Document 3. In addition, the inventors evaluated the pressure loss due to the insertion of the heat transfer promoter into the pipeline in this experiment. From the results of this numerical simulation, in order to improve the heat transfer efficiency in a heat transfer promoter having a plurality of protrusions on the outer circumference, the distance (gap) between the inner surface of the conduit of the radiant tube and the tip of the protrusion of the heat transfer promoter The present inventors have found that it is effective to keep ΔL) at a specific ratio.

In addition, the inventors have found that it is preferable to simply arrange the heat transfer promoter in the pipeline while forming the gap ΔL. Then, the inventors have obtained the finding that the above configuration has a small pressure loss similar to the heat transfer promoter described in Patent Document 3, and that this heat transfer promoter can be manufactured at low cost. ..
Here, the "heat transfer efficiency" in the present invention refers to the efficiency of the heat transferred to the radiant tube line among the heat transmitted to the radiant tube line derived from the combustion gas and the waste heat discharged as the sensible heat of the exhaust gas. Point to that. If the waste heat discharged from the exhaust gas without being transferred to the pipeline is reduced, the heat transfer efficiency is improved.

Then, in order to solve the problem, one aspect of the present invention is a pipeline heated by a fluid gas flowing in the pipeline and one or two or more arranged in the pipeline along the axis of the pipeline. A radiant tube including the heat transfer promoter, the heat transfer promoter projects from the main body portion arranged on the center side of the pipeline and from the main body portion toward the inner wall surface of the pipeline. A plurality of protrusions are provided, and the plurality of protrusions are formed on the outer periphery of the main body portion so as to be arranged along the circumferential direction of the pipeline, and the plurality of protrusions have a tip portion. It is composed of a plurality of first protrusions facing the inner wall surface of the pipeline with a gap ΔL, and other second protrusions, and the number of the first protrusions is larger than the number of the second protrusions. When the 100% ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the conduit portion in which the heat transfer promoter is arranged is set to x [%]. The gist is that the following equation (1) is satisfied.
0.3% <x <7% ・・・ (1)

According to the aspect of the present invention, it is possible to provide a radiant tube having a heat transfer promoter that can be manufactured at low cost while improving the heat transfer efficiency.

It is a figure for demonstrating the structure of the radiant tube which concerns on embodiment based on this invention. It is sectional drawing for demonstrating the cross section of a conduit and the heat transfer promoter of this embodiment, which were cut at AA' of FIG. It is a schematic view seen from the pipeline axial direction explaining the swirling flow R formed in the vicinity of the inner wall surface. It is a figure explaining the example in the case of providing a cavity in a heat transfer promoter, (a) is a plan view seen from the gas flow direction, (b) is a cross-sectional view of BB'of (a). It is an enlarged view explaining the example which provided the notch in the 2nd protrusion. It is a figure for demonstrating the heat transfer promoter of Example 1 (conventional example). It is a figure for demonstrating the heat transfer promoter of Example 2. It is a figure for demonstrating the heat transfer promoter of Example 2. It is a figure for demonstrating the heat transfer promoter of Example 2. It is a figure which showed the result of having verified the effect of this invention. It is a figure which showed the result of having verified the effect of the gap ΔL. It is a figure which showed the result of having verified the effect by the difference of the pipeline cross section.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Here, the drawings are schematic, and the size and length ratio of each part are different from the actual ones. Further, the embodiments shown below exemplify a configuration for embodying the technical idea of the present invention, and the technical idea of the present invention describes the material, shape, structure, etc. of the constituent parts as follows. It is not something that is specific to something. The technical idea of the present invention may be modified in various ways within the technical scope specified by the claims stated in the claims.

(composition)
As shown in FIG. 1, the radiant tube 100 of the present embodiment includes a conduit 1 through which combustion gas (hereinafter, also simply referred to as gas) flows, a radiant tube burner 2 that generates combustion gas in the conduit 1, and the like. It is provided with a heat transfer promoter 4. The radiant tube 100 may or may not be provided with various exhaust heat recovery devices 5 such as a recuperator and a heat storage burner, and other known parts. The recuperator is a device that exchanges heat between the combustion gas flowing through the radiant tube 100 and the combustion air. In the present embodiment, a case where a plurality of heat transfer promoters 4 are arranged coaxially and the protrusions 42 of the plurality of heat transfer promoters 4 are arranged along the pipeline is illustrated.

(Pipeway 1)
As shown in FIG. 1, the pipeline 1 of the present embodiment has a zigzag shape having a substantially W shape in a side view. That is, the pipeline 1 has four straight pipe portions 1A to 1D arranged one above the other, and the ends of the adjacent straight pipe portions 1A to 1D are connected by curved pipe portions 1E to 1G extending in an arc shape. Form a gas flow path. Reference numeral 6 is a separator member that prevents the space between adjacent straight pipe portions from becoming narrow. Reference numeral 7 is a support member supported by the overhanging portion 3A and suppressing the downward displacement of the pipeline 1.

Further, the pipe line 1 is supported by the furnace wall 3 by fixing the inlet side of the straight pipe portion 1A at the most upstream position and the outlet side of the straight pipe portion 1D at the most downstream position to the furnace wall 3.
Then, the heated body is conveyed along the arrangement direction of the plurality of straight pipe portions 1A to 1D, so that the heated body is indirectly heated by the radiant tube 100. FIG. 2 shows an example of the transport direction of the object to be heated with reference numeral 50. Although FIG. 1 illustrates a case where the plurality of straight pipe portions 1A to 1D are arranged in the vertical direction, the arrangement direction of the plurality of straight pipe portions 1A to 1D may be in the horizontal direction.
Here, the pipeline shape of the radiant tube 100 is not limited to the side view substantially W shape. The conduit shape of the radiant tube 100 may be another shape such as a U type or a straight type.

In the pipeline 1 of the present embodiment, at least the case where the opening cross section of the straight pipe portion 1D in which the heat transfer promoter 4 is arranged has an elliptical shape in which the minor axis and the major axis are different as shown in FIG. 2 is taken as an example. explain. As shown in FIG. 2, it is preferable to arrange the components so that the major axis side faces in the vertical direction. When the opening cross section of the straight pipe portion 1D has an elliptical shape in which the minor axis and the major axis are different, it is preferable that the entire conduit 1 has an elliptical shape in which the minor axis and the major axis are different. However, the present invention can be applied even if the opening cross section of the pipeline 1 has another cross-sectional shape such as a perfect circle or a rectangular shape.

(Radiant tube burner 2)
A gas generating portion 2A of the radiant tube burner 2 is arranged on the inlet side of the pipeline 1. The gas generation unit 2A injects fuel gas and combustion air along the extending direction of the pipeline 1 to generate combustion gas. The generated combustion gas transfers heat to the pipeline 1 while flowing through the pipeline 1 from the inlet side to the outlet side.
The gas generating unit 2A is not particularly limited as long as it can generate combustion gas to be passed through the pipeline 1, and a known burner can be applied.

(Heat transfer promoter 4)
The heat transfer promoter 4 is arranged on the outlet side of the intermediate position in the extending direction in the conduit 1 of the radiant tube 100. The heat transfer promoter 4 is provided in the conduit 1 in order to improve the heat transfer efficiency of the radiant tube 100.

Next, the heat transfer promoter 4 of the present embodiment will be described.
In the present embodiment, a plurality of heat transfer promoters 4 are coaxially arranged along the axis of the pipeline 1. Then, the plurality of heat transfer promoters 4 appropriately adjust the waste heat reduction rate and the pressure loss of the radiant tube 100.
Each heat transfer promoter 4 is integrated with the main body 41 located on the cross-sectional center side of the pipeline 1 (the axial side of the conduit 1) and from the main body 41 to the inner wall surface 1a of the conduit 1. A plurality of protrusions 42 that protrude toward the surface are provided.

The plurality of protrusions 42 are integrally formed on the outer periphery of the main body 41 so as to be arranged along the circumferential direction of the pipeline 1. Then, the heat transfer promoters 4 are arranged in the conduit 1 so that the protrusions 42 of the heat transfer promoters 4 are aligned in the longitudinal direction of the conduit 1. It is preferable to arrange the adjacent heat transfer promoters 4 so as to be in contact with each other.
Each protrusion 42 protrudes outward in the radial direction of the pipeline 1 from the main body 41, and as viewed from the axial direction of the pipeline 1, as shown in FIG. 2, the distance from the main body 41 increases (the wall surface of the conduit 1). The closer to), the smaller the width of the pipeline 1 along the circumferential direction. However, each protrusion 42 is configured so that the shape along the axial direction of the pipeline 1 is the same. As a result, a space is formed between the two adjacent protrusions 42 in the circumferential direction of the pipeline 1, and the distance between the two adjacent protrusions 42 increases as the distance from the main body 41 increases. The contour that defines the cross-sectional shape of each protrusion 42 does not have to be a straight line.

Further, the plurality of protrusions 42 included in one heat transfer promoter 4 are classified into a plurality of first protrusions 42a and second protrusions 42b. The tip of the first protrusion 42a is not in contact with the inner wall surface 1a of the conduit 1, and the tip of the first protrusion 42a is the inner wall surface of the conduit 1 in the radial direction of the conduit 1. It is arranged so as to have a gap ΔL with respect to 1a.
On the other hand, in the present embodiment, in the second protrusion 42b, the tip of the protrusion 42 is in contact with the inner wall surface 1a of the pipeline 1. In this case, the second protrusion 42b can position the heat transfer promoter 4 in the pipeline 1 (positioning of the conduit 1 in the axial direction). In this case, the number of the second protrusions 42b is preferably 2 or more.

However, if the heat transfer promoter 4 can be positioned in the conduit 1 (positioning of the conduit 1 in the axial direction) by other means, the second protrusion 42b can be placed in the conduit 1. There is no secret to contacting the wall surface 1a.
It is preferable that the number of the second protrusions 42b is small. In the present embodiment, the number of the second protrusions 42b is smaller than the number of the first protrusions 42a. Preferably, the number of the second protrusions 42b is 1/3 or less, more preferably 1/4 or less of the number of the first protrusions 42a. However, in order for the second protrusion 42b to position the heat transfer promoter 4 in the conduit 1, the number of the second protrusions 42b needs to be two or more. FIG. 2 illustrates a case where the second protrusions 42b are two, and the heat transfer promoter 4 is supported by its own weight with respect to the pipeline 1 by the two second protrusions 42b located on the lower side. NS.

Further, in the present embodiment, the gap ΔL between the tip end portion of the first protrusion 42a and the inner wall surface 1a of the pipeline 1 facing the tip end portion is defined as follows.
That is, when the 100% ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the straight pipe portion 1D of the conduit 1 in which the heat transfer promoter 4 is arranged is x, the following (1) is satisfied. Set so that the gap is ΔL.
0.3% <x <7% ・・・ (1)
Further, it is more preferable to satisfy the following equation (2).
0.5% <x <4.5% ・・・ (2)

More specifically, an example of the heat transfer promoter 4 of the present embodiment will be described.
As described above, each heat transfer promoter 4 includes a main body 41 and a plurality of protrusions 42 protruding from the outer periphery of the main body 41 toward the inner wall surface 1a.
As shown in FIG. 2, the main body 41 has a columnar shape having a shape similar to the elliptical shape of the opening cross section of the pipeline 1 or a cross section similar to the elliptical shape. Then, the main body 41 is arranged with a columnar shaft (longitudinal direction) parallel to the shaft of the pipeline 1.
The main body 41 limits the area through which the gas flowing in the pipeline 1 flows, and increases the flow velocity of the gas flowing on the outer peripheral side (outer diameter side) of the main body 41.
Further, by providing a plurality of protrusions 42 on the outer periphery of the main body 41, the gas flowing through the outer periphery of the main body 41 is divided into a plurality of parts along the circumferential direction by the protrusions 42, and the gas passing through the outer periphery of the main body 41 is divided into a plurality of protrusions 42 between the adjacent protrusions 42. Gas flows through each space.

The protrusion 42 of the present embodiment has a substantially triangular cross section (triangular when viewed from the axial direction of the conduit 1), and the base thereof is integrally formed with the outer circumference of the main body 41. Further, the protrusion 42 has a thick plate shape (rectangular shape when viewed from the side) having the same cross-sectional shape in the direction parallel to the axis of the pipeline 1 in the longitudinal direction.
As shown in FIG. 2, between the protrusions 42 adjacent to each other along the circumferential direction of the pipeline 1 (when viewed from the axial direction of the pipeline 1), the width becomes wider as the distance from the main body 41 increases. Space S is formed.

Due to the plurality of protrusions 42, the gas flowing around the outer periphery of the main body 41 is unlikely to become a swirling flow, and flows along the axis of the pipe portion 1 in a laminar flow along the space S. That is, by providing the plurality of protrusions 42, individual gas flow paths are formed between the protrusions 42 in the circumferential direction, and gas can flow through the respective gas flow paths.
In FIG. 2, the second protrusion 42b is formed by making the lengths of the two lower protrusions 42 longer than those of the other protrusions 42. The tips of the two protrusions 42b come into contact with the lower surface side of the inner wall of the conduit 1, so that the heat transfer promoter 4 is supported in the conduit 1 at a predetermined position. The heat transfer promoter 4 is more stably positioned in the conduit 1 when the uppermost protrusion 42 is also used as the second protrusion 42b and is brought into contact with the inner wall of the conduit 1. However, it is preferable that the number of the second protrusions 42b is small.

Here, as shown in FIG. 2, the position of the center of gravity P2 of the heat transfer promoter 4 arranged in the conduit 1 is set to the center P1 (center of gravity) of the opening cross section of the conduit 1 by the plurality of second protrusions 42b. It is preferable to set (arrange) them so that they match. When the centers of gravity P1 and P2 of both 1 and 4 are arranged so as to coincide with each other, the center of gravity P2 of the heat transfer promoter 4 and the center of gravity in the cross section perpendicular to the combustion flow direction of the radiant tube 100 coincide with each other to promote heat transfer. It is possible to suppress the bias of the body 4 in the direction of gravity and eliminate the deterioration of the heat transfer performance. It is very effective to match the center of gravity of the heat transfer promoter 4 with the center of gravity in the cross section perpendicular to the combustion flow direction of the radiant tube 100 when the radiant tube shape is elliptical.
Further, in the present embodiment, the first protrusion 42a is formed except for the protrusion 42 constituting the second protrusion 42b, and the tip portions of the plurality of first protrusions 42a and the inner surface of the conduit 1 are connected to each other. The lengths of the first and second protrusions and the dimensions of the main body 41 are set so that a gap ΔL is formed between them.
The gap ΔL satisfies the condition of the above equation (1).

(Action)
Next, the action of the heat transfer promoter 4 of the present embodiment will be described.
The main body 41 limits the area through which the gas flowing in the pipeline 1 flows, and the flow velocity of the gas flowing on the outer peripheral side (outer diameter side) of the main body 41 becomes high. In the present embodiment, the center of gravity of the cross section of the main body 41 and the center of gravity of the cross section of the pipeline 1 are matched or approximated to make the distribution of the gas flowing on the outer circumference of the main body 41 more even.
Further, the space around the main body 41 is divided into a plurality of spaces along the circumferential direction of the pipeline 1 by the plurality of protrusions 42. That is, independent gas flow paths are formed between the adjacent protrusions 42, and gas can flow through each gas flow path.

Here, the ratio of the cross-sectional area of the heat transfer promoting body 4 to the opening cross-sectional area of the conduit 1 portion in which the heat transfer promoting body 4 is arranged is set to A, and the opening cross section of the conduit 1 portion in which the heat transfer promoting body 4 is arranged. When the ratio of the peripheral length of the cross section of the heat transfer promoter 4 to the peripheral length of the above is B, the heat transfer promoter 4 with respect to the conduit 1 satisfies the following equations (3) and (4). Is preferable.
A ≤ 0.53 ・・・ (3)
(1-A) ^-4/5 × A ・ B ≧ 2.48 ・・・ (4)

The equations (3) and (4) will be described.
Here, let α be the area of the opening cross section formed by the installation portion of the pipeline 1. Further, the cross-sectional area of the heat transfer promoter 4 is β. At this time, A is (β / α). Further, let c be the peripheral length of the opening cross section of the installation portion of the pipeline 1 (the inner peripheral length of the pipeline 1). Further, the peripheral length of the heat transfer promoter 4 is d. At this time, B is (d / c).
The heat transfer promoter 4 of the present embodiment is preferably designed so that A and B satisfy the above formulas (4) and (4). As a result of examination by the inventors, it was found that when the above-mentioned A exceeds 0.53, the pressure loss is large and the flow of combustion gas is remarkably suppressed. Therefore, as specified in the formula (3), A is preferably 0.53 or less. More preferably, A is 0.46 or less.

Further, in the above equation (4), when the present inventors reduce the cross-sectional area of the heat transfer promoter 4 based on a general convection heat transfer theoretical equation, the gas flow velocity becomes slow and the effect of convection heat transfer becomes effective. This equation was found by paying attention to the fact that the heat transfer area is weakened and the heat transfer area is proportional to the outer peripheral length of the heat transfer promoter 4. Then, the present inventors have confirmed that the desired heat transfer efficiency can be obtained when the left side of the formula (4) is 2.48 or more.
Further, one of the features of the present embodiment is that a predetermined gap ΔL is provided between the first protrusion 42a and the inner wall surface 1a of the pipeline 1.
By providing the above gap ΔL in the vicinity of the inner wall surface 1a of the pipeline 1, as shown in FIG. 3, the direction of rotation of the combustion flow along the circumferential direction of the pipeline 1 with respect to the vicinity of the inner wall surface of the pipeline 1. Flow (swirl flow R) is formed.

Here, if the flow velocity in the flow direction of the combustion flow is Vx and the flow velocity in the cross section perpendicular to the flow direction is Vy and Vz, the velocity V of the combustion flow can be expressed by the following equation (5).
V = √ (Vx ² + Vy ² + Vz ² ) ・・・ (5)
As can be seen from the equation (5), the velocity V is increased by the amount of the swirling flow R formed in the vicinity of the inner wall of the pipeline 1, and the heat transfer efficiency is further improved in the present embodiment.

Also, the swirling flow R becomes stronger especially when the flow shifts from a curved surface to a straight surface. The portion where the flow shifts from the curved surface to the straight surface is, for example, the transition portion from the curved pipe portion 1G to the straight pipe portion 1D in FIG. Stagnation is likely to occur at the spatial position. This is due to the bias of the flow caused by the separation of the combustion flow on the curved surface. Therefore, in a heat transfer promoter having no gap or a small gap for which the gap ΔL is based on the present invention, different amounts of combustion gas flow between the divided spaces S, resulting in a decrease in heat transfer efficiency. On the other hand, by providing an appropriate gap ΔL, the flow rate balance between the plurality of spaces S partitioned by the protrusions 42 becomes naturally the same. In the present embodiment, the protrusion 42 that divides the gas flow has a shape that becomes smaller as it approaches the inner wall surface 1a of the pipeline 1. Therefore, as shown in FIG. 3, a swirling flow is likely to occur even in each space S partitioned by the protrusions 42, and the heat transfer efficiency from the combustion flow to the heat transfer promoter increases.

Further, in the present embodiment, the cross section of each space S partitioned by the protrusions 42 becomes wider as it approaches the inner wall surface 1a of the pipeline 1, and the influence of the wall surface is small, so that the flow path resistance is relative. Is small. Therefore, the gas flowing between the protrusions 42 flows on the outer peripheral side rather than the central side. As a result, more gas contributes to the swirling flow R formed in the vicinity of the inner wall surface 1a of the pipeline 1.

In particular, in the present embodiment, the shape of the protrusion 42 is not a rectangular shape in cross section, but a substantially triangular shape in which the width in the circumferential direction becomes narrower as it approaches the inner wall of the pipeline 1. For this reason, the cross section of each space S partitioned by the protrusion 42 is in the circumferential direction per unit length as it goes outward in the radial direction, as compared with the case where the shape of the protrusion 42 is rectangular in cross section. The degree of spread can be set large. As a result, the gas flowing between the protrusions 42 flows closer to the outer peripheral side than to the central side, so that more gas contributes to the swirling flow R formed in the vicinity of the inner wall surface 1a of the pipeline 1.

The protrusions 42 preferably have a shape (continuous shape) in which the roots of adjacent protrusions 42 (parts on the main body side) are connected to each other.
Further, if the cross section of the space S formed between the protrusions 42 is triangular, it is always aligned with the heat transfer promoter 4, the combustion gas, and the wall surface of the conduit 1, so that radiation is transmitted from the combustion gas, which is a heat source, to the conduit. Does not inhibit heat.
Here, in order for the swirling flow R to occur in the vicinity of the inner wall surface 1a of the pipeline 1, a predetermined gap ΔL is required between the protrusion 42 of the heat transfer promoter 4 and the inner wall surface 1a of the conduit 1. NS. The predetermined gap ΔL is a gap called the viscous bottom layer in which the flow velocity of the combustion gas near the wall surface is equal to or greater than the region width close to zero.

In the in-pipe flow of a general industrial radiant tube, the region width of the viscous bottom layer is 0.3% or more with respect to the equivalent diameter, and 0.5% with respect to the equivalent diameter is sufficiently within the transition region.
Therefore, in the present embodiment, the 100% ratio x of the above-mentioned gap ΔL ratio (ΔL / Dt) to the equivalent diameter Dt of the conduit 1 portion in which the heat transfer promoter 4 is arranged is set to 0.3% or more. Preferably, it was 0.5%.
On the other hand, if the gap ΔL is too wide, the heat transfer area, particularly the convection heat transfer area from the combustion flow to the heat transfer promoter, becomes small. Therefore, the above x is set to 7% or less, preferably 4.5% or less.

Here, as the material constituting the heat transfer promoter 4, a material known as the heat transfer promoter 4 may be adopted. For example, examples of the material include refractory heat insulating bricks, refractory metals, ceramics, and castables. In order to reduce the production cost and suppress the deformation of the radiant tube 100 by the weight of the heat transfer promoter 4, it is preferable to use a refractory heat insulating brick that is inexpensive and lightweight.

As described above, in the present embodiment, the heat transfer promoter 4 is designed to have a specific shape as described above. As a result, the cross-sectional area of the flow path can be narrowed, and the flow velocity of the combustion gas can be increased by reducing the flow path. Further, in the present embodiment, the heat transfer efficiency can be improved without suppressing the swirling flow R in the vicinity of the inner wall surface of the combustion gas while increasing the heat transfer area of the heat transfer promoter 4. Further, since the heat transfer promoter 4 of the present embodiment has a simple shape, it can be manufactured at low cost. Further, by inserting the heat transfer promoter 4 into the radiant tube 100, the combustion gas can be agitated as in the prior art. In the above description, the heat transfer promoter 4 having a uniform cross section is used along the flow path, but the agitation of the combustion gas can be further promoted by tapering the upstream side of the exhaust gas along the flow path. , The heat transfer efficiency can be further improved.

[About equivalent diameter]
The equivalent diameter Dt can be obtained by the following formula from the peripheral length L of the inner wall and the opening cross-sectional area Sa of the pipeline 1 perpendicular to the flow direction.
Dt = (4 ・ Sa) / L

[Approximate method of obtaining the viscous bottom layer of circular tube flow]
The coefficient of friction f is expressed by the following equation from Colebrook's equation.
1 / √f = -2log ₁₀ (((ε / Dt) /3.7)
+ (2.51 / (Re√f)))
here,
ε: Surface roughness Re: Reynolds number (obtained by (u · Dt) / ν)
Is.

Further, assuming that the pressure drop per unit length in the cross section of the circular pipe is ΔP,
It can be expressed as ΔP = 1/2 (f · (1 / Dt) · ρ · u ^2).

_{Since the shear stress τ 0} generated on the inner wall surface 1a of the pipeline 1 per unit length and the pressure drop ΔP are equal, it can be described as follows.
Sa ・ ΔP = L ・ τ ₀
τ ₀ = (Sa / (2 ・ l ・ Dt)) f ・ ρ ・ u ²
The friction velocity u _* can be expressed as u _* = √ (τ _{0 / ρ).}
The range of the viscous bottom layer is u _* (y / ν) <5.

Therefore, the gap ΔL of the present embodiment may be larger than the viscous bottom layer, and may be set as follows.
x [%] x 100 = d / Dt> 5 (ν / (u _*・ Dt))
≒ 0.003 or (0.005)

(Modification example)
(1) The cross-sectional shape of the tip of the protrusion 42 is preferably a curved surface shape such as a chamfered shape or a rounded shape.
The position of the heat transfer promoter 4 near the inner wall surface 1a of the pipeline 1 is the tip of the protrusion. By blunting the contour shape by making the tip a chamfered shape or the like, the area of the facing portion of the inner wall surface 1a of the pipeline 1 in the protruding portion is increased.
As a result, the heat transferred from the combustion gas to the heat transfer promoter 4 is efficiently transferred from the tip of the protrusion 42 approaching the inner wall surface 1a of the conduit 1 to the inner wall surface 1a of the conduit 1. improves. That is, the heat transfer area of the heat transfer promoter 4 to the conduit 1 is increased, and a further heat transfer promotion effect is exhibited.

(2) As shown in FIG. 4B, for example, the heat transfer promoter 4 has a hollow inside, and the hollow opens on the surface side along the moving direction of the fluid flowing through the conduit 1. doing.
According to this configuration, it is possible to reduce the weight of the heat transfer promoter 4 while maintaining a large heat transfer area of the heat transfer promoter 4.

(3) As described above, the opening cross section of the conduit 1 portion where the heat transfer promoter 4 is arranged may have an elliptical shape in which the minor axis and the major axis have different lengths, and the major axis may be arranged in the vertical direction. No.
The atmosphere in which the radiant tube 100 is arranged becomes a high temperature atmosphere, and a heat load is applied to the pipe line 1. In this modified example, the rigidity of the pipe line 1 is improved, and the load and heat load of the heat transfer promoter 4 are applied to the pipe line 1. It is possible to suppress the deformation of the pipeline 1 even if it is loaded on the pipe. This makes it possible to stably perform indirect heating from the radiant tube 100 to the object to be heated for a longer period of time.

(4) The number of the first protrusions 42a is preferably 8 or more and 25 or less, for example.
As the number of protrusions 42 increases, the number of flow paths formed on the outer periphery of the main body 41 increases, and it becomes easier to adjust the flow in the uniaxial direction of the pipeline along the circumferential direction. However, if it is too large, the flow path resistance may increase, so 25 or less is preferable.

(5) Further, it is preferable that one or more first protrusions 42a are arranged between two adjacent second protrusions 42b.
It is possible to suppress the reduction of the location where the swirling flow R is generated along the circumferential direction.
A notch 42Ba as shown in FIG. 5 is formed at an intermediate position in the longitudinal direction with respect to the tip of the second protrusion 42b that comes into contact with the surface of the pipeline 1, and the swirling flow is caused by the second protrusion 42b. The suppression of the flow of R may be reduced. The distance ΔL1 facing the inner wall surface 1a of the pipeline 1 in the notch 42Ba is set within the same range as the condition facing the inner wall surface 1a of the gap ΔL. That is, it is preferable to set so as to satisfy the equation equivalent to the equation (1) above.

(6) The body to be heated is conveyed along the arrangement direction of the plurality of pipelines 1 and indirectly heated by the radiant tube 100. When the cross section of the conduit 1 is elliptical, the heating efficiency is better when the major axis is set in the alignment direction of the conduit 1.
It is preferable that the area of the space between the protrusions 42 arranged on the side facing the heated body is set to be relatively larger than the area of the space between the protrusions 42 at other positions. For example, the minor axis of the ellipse is divided into four regions by two straight lines tilted ± 45 degrees around the center of the ellipse, and the area of the space between the protrusions 42 located in each compartment is divided. So that the total area of the space in the section (the section including the minor axis in the ellipse) arranged on the side facing the object to be heated is relatively larger than the total area of the space in the other sections. Set.

(effect)
This embodiment has the following effects.
(1) In the present embodiment, the conduit 1 heated by the fluid gas flowing in the conduit 1 and one or more heat transfer arranged in the conduit 1 along the axis of the conduit 1. A radiant tube 100 including a facilitator 4, the heat transfer facilitator 4 has a main body 41 arranged on the center side of the conduit 1 and projects from the main body 41 toward the inner wall surface 1a of the conduit 1. The plurality of protrusions 42 are formed on the outer periphery of the main body 41 so as to be arranged along the circumferential direction of the pipeline 1, and the plurality of protrusions 42 are formed at the tips thereof. The portion is composed of a plurality of first protrusions 42a having a gap ΔL with the inner wall surface 1a of the pipeline 1 and facing each other, and other second protrusions 42b, and the number of the first protrusions 42a is 100 minutes of the ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the pipe 1 portion in which the heat transfer promoter 4 in the pipe 1 is arranged, which is set to be larger than the number of the second protrusions 42b. When the rate is x [%], the following equation is satisfied.
0.3% <x <7%

According to this configuration, it is possible to provide a radiant tube 100 having a heat transfer promoter 4 that can be manufactured at low cost while improving heat transfer efficiency.
In particular, according to this configuration, although the heat transfer promoter 4 has a simple structure, a swirling flow R that contributes to heat transfer can be easily formed in the vicinity of the inner wall surface 1a of the pipeline 1, resulting in high heat transfer efficiency. improves.

(2) In the present embodiment, the tip of the second protrusion 42b comes into contact with the inner wall surface 1a of the pipeline 1, so that the heat transfer promoter 4 is positioned with respect to the conduit 1. In this case, the number of the second protrusions 42b is 2 or more.
According to this configuration, the heat transfer promoter 4 can be easily arranged in the pipeline 1 while forming a gap ΔL between the first protrusion 42a and the inner wall surface 1a.
The tip of the second protrusion 42b does not have to be in contact with the inner wall surface 1a of the pipeline 1. In this case, the gap between the tip of the second protrusion 42b and the inner wall surface 1a of the pipeline 1 does not have to satisfy the gap ΔL.

(3) In the present embodiment, the heat transfer promoter 4 is installed so that the center of gravity P2 of the heat transfer promoter 4 coincides with the center P1 (center of gravity) of the opening cross section of the pipeline 1.
By arranging the two so that the centers of gravity coincide with each other, the center of gravity of the heat transfer promoter 4 and the center of gravity in the cross section perpendicular to the combustion flow direction of the radiant tube 100 coincide with each other, and the heat transfer promoter 4 moves in the direction of gravity. It is possible to suppress the bias of the heat transfer and eliminate the deterioration of the heat transfer performance.

(4) In the present embodiment, the cross-sectional shape of each protrusion 42 is such that the width along the circumferential direction of the conduit 1 becomes smaller as the distance from the main body 41 along the radial direction of the conduit 1 decreases. Therefore, a space is formed between the two adjacent protrusions 42 in the circumferential direction of the pipeline 1 so that the distance between the two adjacent protrusions 42 increases as the distance from the main body 41 increases.
According to this configuration, even if a space is formed between the two protrusions 42 so that the distance between the two adjacent protrusions 42 increases as the distance from the main body 41 increases, the protrusions 42 have a cross-sectional plate shape. As a result, the gas flow flows to the outer peripheral side more reliably, and the swirling flow R due to the gap ΔL at the tip of the protrusion 42 is formed more reliably, and as a result, the heat transfer efficiency can be further improved.

(5) In the present embodiment, the shape of the tip of the protrusion 42 is a chamfered shape or a curved surface shape.
According to this configuration, the heat transfer efficiency from the protrusion 42 to the conduit 1 is further improved.
(6) The heat transfer promoter 4 has a hollow inside, and the hollow may have a shape in which a surface facing the moving direction of the fluid flowing through the conduit 1 is closed.
According to this configuration, the weight of the heat transfer promoter 4 can be reduced, and the deformation of the pipeline 1 due to the heat load can be further suppressed.

(7) In the present embodiment, the opening cross section of the conduit 1 portion in which the heat transfer promoter 4 is arranged has an elliptical shape. The size of the ellipse is different between the minor axis, which has the shortest diameter, and the major axis, which is the diameter orthogonal to the minor axis. It is preferable that the major axis of the ellipse faces in the vertical direction.
According to this configuration, the rigidity of the conduit 1 is improved, the deformation of the conduit 1 due to the heat load is further suppressed, and the heat transfer efficiency by the heat transfer promoter 4 of the present embodiment can be further improved.
For the ellipse, for example, (major diameter Lb / minor diameter La) is 1.1 or more and 1.6 or less.

(8) The cross-sectional shape of each heat transfer promoter 4 in the longitudinal direction is the same, the shapes of the plurality of heat transfer promoters 4 are the same, and the plurality of heat transfer promoters 4 are coaxial and each tip portion. It is preferable to arrange the positions so that they are aligned in the axial direction.
In this case, the swirling flow R can be more reliably generated only in the vicinity of the inner wall surface 1a of the pipeline 1, and the heat transfer efficiency can be further improved even with the heat transfer promoter 4 having a simple structure. Become.

Hereinafter, examples based on the embodiments will be described.
In this example, the heat transfer accelerator 4 used in the radiant tube 100 was evaluated by the combustion heat transfer simulation using the following finite volume method.
(I) Pipeline 1
The shape of the pipeline 1 in the extending direction was the W shape shown in FIG. 1, and the opening cross section of the pipeline 1 was an elliptical shape having a major axis of 236 mm and a minor axis of 188 mm. The total length of the pipeline 1 is 8900 mm.
(Ii) Gas generator 2A
A burner was used as the gas generating unit 2A. The fuel used was a refined gas generated during the carbonization of coal in a coke oven.
(Iii) Heat transfer promoter 4
It is assumed that 10 heat transfer promoters 4 are arranged from the position of 300 mm on the exit side of the radiant tube 100 of the straight pipe portion located at the most downstream to the position of 950 mm.

(Iv) Waste heat reduction ratio As the waste heat reduction ratio, the balance between the amount of heat radiated from the test furnace and the amount of heat of the exhaust gas was calculated, and the ratio of the amount of heat of the exhaust gas to the amount of heat input was calculated. Then, the ratio when the waste heat reduction rate is 1.00 when the total protrusions 42 of the heat transfer promoter 4 of Example 1 described later are in contact with the inner wall of the radiant tube 100 (see FIG. 6) is shown.
In this example, when the waste heat reduction ratio is 1.20 or more, preferably when the waste heat reduction ratio is 1.50 or more, the heat transfer efficiency is excellent and the result is passed.

First, the basic shape of the heat transfer promoter 4 having a star-shaped cross section was examined.
In Example 1 shown in FIG. 6, all the tips of the plurality of tips of the heat transfer promoter 4 and the inner wall of the pipeline 1 are in contact with each other.
In Example 2 shown in FIG. 7, the tip portion of the heat transfer promoter 4 is evenly shortened. However, the heat transfer promoter 4 is biased in the direction of gravity. That is, the position of the center of gravity of the heat transfer promoter 4 is located below the center of the cross section of the pipeline 1.

In Example 3 shown in FIG. 8, only the two tip portions have the same length as in Example 1 as compared with Example 2, and the center of gravity of the heat transfer promoter 4 and the center of the conduit 1 (on the cylinder) are set as the second protrusion 42b. The center of gravity of the cross section with respect to the direction perpendicular to the flow direction of
In Example 4 shown in FIG. 9, the tip of the protrusion 42 is chamfered so that the gap ΔL at the tip of the protrusion 42 is the same as that of Example 3 from the shape of Example 1. In addition, in the shape shown in FIG. 9 of the protrusion 42, even when R was taken for the protrusion 42, the amount of waste heat reduction was almost the same as that of Example 4.

The examination results of Examples 1 to 4 described above are shown in FIG. In FIG. 10, the vertical axis represents the waste heat reduction ratio.
As can be seen from FIG. 10, by providing a gap ΔL at the tip of the protrusion 42 as in Examples 2 to 4, waste heat is wasted as compared with the state where the tip is in contact with the pipeline 1 (Example 1). It was found that the reduction ratio improved.
Further, as in Examples 3 and 4, by matching or approximating the center of gravity of the cross section of the pipeline 1 and the center of gravity of the cross section of the heat transfer promoter 4, the waste heat reduction ratio is further improved and the waste heat reduction ratio is increased. It became 1.50 or more.

Next, based on the shape of Example 4, the waste heat reduction ratio was examined by changing the gap ΔL between the tip of the star-shaped heat transfer promoter 4 and the inner wall of the pipeline 1.
The result is shown in FIG.
As can be seen from FIG. 11, if the gap ΔL between the tip of the protrusion 42 and the inner wall of the tube with respect to the equivalent diameter of the inner wall of the radiant tube 100 satisfies 0.3 <x <7, the waste heat reduction ratio is 1.3 times or more, which is extremely high. It was confirmed that it shows a high effect of improving heat transfer efficiency. More preferably, it was confirmed that if the gap ΔL between the tip portion and the inner wall satisfies 0.5 <x <4.5, the waste heat reduction ratio is 1.5 times or more, and a higher heat transfer efficiency improving effect is exhibited.

Next, the one having a perfect circular shape with a diameter of 188 mm and the one having an elliptical shape were compared.
In either case, the gap ΔL between the tip of the protrusion 42 and the inner wall of the tube with respect to the equivalent diameter of the inner wall of the radiant tube 100 is based on the amount of waste heat when the tip of the heat transfer promoter 4 is in contact with the wall surface of the pipeline 1. It is a condition that a perfect circle and an ellipse are equal.
The comparison result is shown in FIG.
As can be seen from FIG. 12, it was found that the waste heat reduction ratio is similarly improved regardless of whether the opening cross section of the pipeline 1 is circular or elliptical. Furthermore, the elliptical opening cross section of the pipeline 1 has a circular shape. It was found that the waste heat reduction ratio was improved by about 10% as compared with the case of.

Here, the entire contents of the Japanese patent application 2020-028033 (filed on February 21, 2020), for which the present application claims priority, form a part of the present disclosure by reference. Although the description has been made with reference to a limited number of embodiments, the scope of rights is not limited thereto, and modifications of each embodiment based on the above disclosure are obvious to those skilled in the art.

1 Pipeline 1a Inner wall surface 2A Gas generating part 3 Furnace wall 4 Heat transfer promoter 41 Main body part 42 Protruding part 42a First protruding part 42b Second protruding part 100 Radiant tube R Swirling flow ΔL Gap

Claims

A radiant tube comprising a pipeline heated by a fluid gas flowing through the pipeline and one or more heat transfer promoters arranged along the axis of the pipeline in the pipeline.
The heat transfer promoter includes a main body portion arranged on the center side of the pipeline and a plurality of protrusions protruding from the main body portion toward the inner wall surface of the pipeline.
The plurality of protrusions are formed on the outer periphery of the main body so as to be arranged along the circumferential direction of the pipeline.
The plurality of protrusions are composed of a plurality of first protrusions whose tip portions face each other with a gap ΔL with the inner wall surface of the pipeline, and other second protrusions.
The number of first protrusions is set larger than the number of second protrusions,
When the 100% ratio (ΔL / Dt) of the gap ΔL to the equivalent diameter Dt of the pipeline portion where the heat transfer promoter is arranged in the pipeline is x [%], the following (1) A radiant tube characterized by satisfying the formula.
0.3% <x <7% ・・・ (1)
The radiant tube according to claim 1, wherein the tip of the second protrusion comes into contact with the inner wall surface of the pipeline.
The radiant tube according to claim 1 or 2, wherein the heat transfer promoter is installed so that the center of gravity of the heat transfer promoter coincides with the center of the opening cross section of the pipeline.
The cross-sectional shape of each of the protrusions is such that the width along the circumferential direction of the pipeline becomes smaller as the distance from the main body is along the radial direction of the conduit. Any of claims 1 to 3, wherein a space is formed between the two protrusions adjacent to each other in the direction so that the distance between the two adjacent protrusions increases as the distance from the main body increases. The radiant tube described in item 1.
The radiant tube according to any one of claims 1 to 4, wherein the shape of the tip of the protrusion is a chamfered shape or a curved surface shape.
The heat transfer promoter has a hollow inside, and the hollow has a shape in which a surface facing the moving direction of the fluid flowing through the pipeline is closed. The radiant tube according to any one of 5.
The radiant tube according to any one of claims 1 to 6, wherein the opening cross section of the conduit portion in which the heat transfer promoter is arranged is elliptical.